TECHNO CA L NOTE NUMBER 259
UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE
FOREST P S LABORATORY
MADISON 5. WISCONSIN C February 1956
TEMPERATURES NECtSRY TO KILL FUNGI I WOOD
Work at the Forest Products Laboratory has shown that fungi in wood are killed by heat most effectively when the moisture content of the wood is above the fiber saturation point. The data in table I were obtained for wood infected with Lenzites sepiaria, Lentinus lepideus, and Poria incrassata, 1 all prominent decay fungi. The moisture content of the wood was kept above the fiber saturation point while the heat was applied.
Table 1. --Recommended times at various temperatures to kill fungi in
Wood heated in : Wood heated in air
steam or equivalent :-----------------------------------------90 to 97 percent 35 to 40 percent
: relative humidity : relative humidity
Temperature: Time : Temperature : Time :Temperature : Time
OF. : Min. : F. : Min. : F. : M.
150 .- 60 : 150 :100:
170 : 30 : 170 : 30 : 170 : 50
180 2 20 180 : Z0
212 : 5 ::::
*The temperature is that of the wood, not that at the surface of the wood.
--Chidester, Mae S. Temperatures Necessary to Kill Fungi in Wood.
Proc. Amer. Wood-Preservers, Assn. 33:316-324. 1937.
In a later series of tests2 that involved 6 fungi and 5 wood species, a similar time-temperature relationship was found. The following is a listing of the fungi used and their source: Wood and locality from
Fungus* which obtained
Lentinus lepideus Fr. Jack pine (Pinus banksiana) Canada
Lenzites sepiaria (Wulf.) Fr. : Eastern hemlock (Tsuga canaden.sis) : Wisconsin
Poria incrassata (B. and C.) Burt.: Southern yellow pine, Virginia Fomes roseus Fr. : Jack pine (Pinus banksiana) Canada
Lenzites trabea (Pers.) Fr. : Western redcedar (Thuja plicata) : Wisconsin
Trametes serialis Fr. : Douglas-fir (Pseudotsuga menziesii)
*The first 3 fungi are the same strains as used in the first studies.
Chidester, Mac S. Further Studies on Temperatures Necessary to Kill
Fungi in Wood. Proc. Amer. Wood-Preservers' Assn. 35: 319-324.
Table Z presents the time-temperature relationships recommended on the basis of the second series of tests.
Table 2. --Recommended times at various temperatures to kill fungi in green wood
Wood heated in steam or an equivalent
SF. : Min.
150 : 75
170 : 30
180 : 20
200 : 10
212 : 5
*Internal temperatures, not temperatures at the
surface of the wood.
The recommended heating periods were based on the time after the wood had reached 150* F. These periods provide a margin of safety in that they are somewhat longer than the studies indicated were necessary for sterilization.
The recommendations in table 2 coincide with those in table I except that the heating period at 150* F. was increased from 60 to 75 minutes because of the longer time needed to kill Lenzites trabea. Work at the Forest Products Laboratory has shown- that these recommendations are easily met by ordinary commercial treatments of green wood when the preservative temperature is above 150* F.
It does not appear practical to sterilize wood at internal temperatures lower than 150' F. The most resistant fungi tested were not killed after 12 hours at 140*, 20 hours at 131*, or 24 hours at 122* F.
.-Mac Lean. J. D Comments on: Temperatures Necessary to Kill Fungi
in Wood. Proc. Amr. Wood Prestere crs' Assn. ~. 324 2. I >7
Z M r79t *
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